The invention relates to a system for controlling the propulsion on motor vehicles as described in copending U.S. patent application Ser. No. 136,931 filed Dec. 23, 1987, which issued as U.S. Pat. No. 4,785,904.
In this known system, a reduction of the drive torque is effected when the slip of at least one driven vehicle wheel exceeds a preset threshold value. As soon as the wheel tending to spin no longer accelerates, the torque is increased to a value calculated from various input variables.
The process for detecting wheel slip of a vehicle with all wheel drive is known from EPO No. 229,249A1, in which the slip values of the individual driven wheels are determined from the calculated angular speed change and the comparison of the calculated angular speed change with the values actually measured. The calculation of the angular speed change to be expected on the basis or the load requirement is made by specific data, inter alia, stored in an engine characteristic graph.
Control signals such as wheel slip or wheel acceleration derived from wheel speed sensors are insufficient for optimum control, in particular when starting to move. The dynamics of the wheels is not in phase with the dynamics of the engine, and utilizable control signals arise only above a certain wheel circumferential speed of approximately 3 km/h.
Related to a control signal obtained from a wheel sensor, the engine has a delayed reaction to an adjustment of the throttle valve or an adjustment of the fuel injection amount, in particular when the drive torque is increased.
With a rapid increase in speed, it is difficult to correct the excess torque generated at the driven wheel. Especially when accelerating from a stationary position, a great excess of torque often arises very quickly before utilizable wheel speed signals are present. This is undesirable, since the traction is considerably reduced, for example in the case of low adhesion coefficients.
Control signals used for known systems arise when preset slip or acceleration limits are exceeded and are determined with the aid of wheel speed sensors.
It is the object of the invention to improve known systems for propulsion control such that in particular when accelerating from a stationary position, it is possible for the control to begin at an early point and prevent an excess of torque.
This object is achieved according to the invention by the following features. According to this, a control signal is generated by a first device if, when the engine speed is increasing, the vehicle longitudinal acceleration, measured by a sensor arranged on the vehicle, does not increase, that is to say remains constant or decreases.
In this manner, the range of the maximum adhesion coefficient is attained. In particular in the case of a smooth roadway, this state can already be established long before a utilizable signal is available from the wheel speed sensors and this signal exceeds a preset threshold value. This time span gained can be used for cutting off the drive torque early, which results in considerably less excess torque, which can then be controlled well.
Further, the control signal of the first device, depending on the engine type used (Otto engine with carburetor or fuel injection or diesel engine), is used for at most the preset time span or, as long as the engine speed does not again fall below values stored at the moment the interruption began, to interrupt the ignition (in the case of an Otto engine) or the fuel injection system (in the case of an Otto or diesel engine). Subsequently, or after the appearance of a control signal derived from the speed sensors (exceeding a slip or acceleration threshold), the control signal is used to set the ignition or the throttle valve or the fuel injection system to the value which is associated with the measured (maximum) value of the vehicle longitudinal acceleration or, a slightly lower value.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.